When a mechanical fastener driver is used to insert or to remove a threaded fastener, rotational force or torque is applied to the fastener to cause it to rotate. In this manner, the fastener can be driven into or removed from a work piece. In the orthopedic surgical arts, the work piece is usually bone. There exist in the orthopedic surgical arts applications in which threaded fasteners are inserted into and removed from bone. As in other fields, there exists the need in some of these applications to control the torque applied via the driver to the fastener. For example in the orthopedic surgical arts, it is common for a threaded fastener to be driven into a human bone. A universal problem in the field is that when the torque applied to the driver is too great, the bone at the work site may be permanently damaged by the fastener. Also, where one surgeon may successfully drive the screw into the work site, a different surgeon or the same surgeon on a different occasion may apply too great a force to the fastener, damaging the bone. Additionally, in some surgical procedures, if the fasteners are set with insufficient torque, this can result in a bad outcome as well.
Thus, there is a continuing need in the orthopedic surgical field for mechanical drivers adapted for specific surgical applications in which the torque transmitted via the driver to the orthopedic fastener is controlled such that different operators of the driver cannot exceed a predetermined torque when using a driver for that application. The field has been motivated to address this need and torque-limiting drivers are available for orthopedic use.
However, a continuing problem in the industry is that, although the calibration of such instruments can be accurately set during their production, once in use in the field, their repeated use, cleaning and sterilization (heat and chemical) gradually alters the calibration setting of these instruments and shortens their useful service life. It would be beneficial in the orthopedic surgery industry to have available an alternative calibrated torque-limiting fastener driver adapted for orthopedic surgical use that has an extended accurate calibration service life.